Hydrocarbon conversion of paraffin hydrocarbons to produce olefins and recycling theolefin hydrocarbons containing less than 11 carbon atoms



United States Patent 3 221 077 HYDRGCARBON CONQEFZSEON 0E IARAFFEN HY- DRQCARBONS T6 PRGDUCE OLEFENS AND RECYCLING THE @LEFIN HYDRGCARBGNS CONTAINING LESS THAN 11 CARBQN ATGM Clarence L. Dulaney and Marvin Lee Owens, J12, Texas City, Tex, assignors to li ionsanto Company, a corporation of Delaware No Drawing. Filed Apr. 18, 1963, Ser. No. 273,859 18 Claims. (Cl. 260683) The present invention relates to a process for the thermal cracking of paraffin hydrocarbons. More particularly, the present invention relates to a process for the thermal cracking of paralfin hydrocarbons whereby the yield of higher molecular weight olefinic hydrocarbons suitable for the preparation of alkyl aromatic hydrocarbons for detergent use is significantly increased.

Presently, there is an ever increasing demand for alkyl aromatic hydrocarbons, particularly alkyl benzenes. These alkyl aromatics contain an aromatic nucleus and an alkyl substituent of 10 to 20 carbon atoms, More often, the alkyl substituents are of approximately 11 to 15 carbon atoms. The alkyl substituents are obtained either by the polymerization of lower molecular weight olefins, dehydrogenation of paraffins within the proper molecular weight or the cracking of high molecular weight paraflinic feedstocks, as well as other methods. The cracking of high molecular weight paraffinic feeds, both thermally and catalytically, produce materials ranging from methane to high molecular weight waxy solids. Among the olefins produced by cracking are those ranging in carbon number from 2 up to and higher, depending largely upon feedstock. For use in the preparation of alkyl aromatics for the detergent industry, it is generally desirable to maximize the production of the olefins in the C plus molecular Weight range, particularly the C to C olefins.

It is an object of the present invention to provide an improvement in the process of thermally cracking relatively high molecular weight paraflinic feedstocks. Another object of the present invention is to provide a process for obtaining increased yields of olefin hydrocarbons of 11 carbon atoms and above by the thermal cracking of relatively high molecular weight parafiinic feedstocks. Additional objects will become apparent from the following description of the invention herein disclosed.

In fullfillment of these and other objects, it has been found that when the liquid olefinic material of below 11 carbon atoms obtained from the thermal cracking of high molecular Weight paraifinic feedstocks is recycled to the thermal cracking zone, there is a significant increase in the ultimate yield of olefin hydrocarbons of 11 carbon atoms and greater.

In order to demonstrate the present invention as well as to further describe its operation, the following examples are presented. These examples are in no way to be construed as limiting the present invention.

Example I Two thermal cracking runs were made using as a feed a parafiin wax having a molecular weight range of from about to 700 and a boiling range of 50 to 400 C. In one of the runs no recycle was returned to the thermal cracking zone while in the other a C C olefin fraction was returned to the thermal cracking zone. The C -C olefin fraction was one having a boiling range of from approximately 135 C. at 760 rnrn./Hg to 119 C. at 100 mm./ Hg and had a composition as follows:

3,221,077 Patented Nov. 30, 1965 Mono-olefins Di-olefins Tri-olefins 2. 2 2. 6 0. 3 23. 3 4. 2 1. 1 58. l 2. 5 0. 6 C11 4. 5 O. 3

Totals 88. l 9. 6 2. 0

The amount of C C recycled to the thermal reaction zone was approximately 5% of the total feed to the thermal reaction zone. Both of the thermal cracking runs were carried out in a 35 foot, inch stainless steel tube. The conditions and results of these two runs are set out in the table below:

Example 11 Two additional thermal cracking runs were made under the same conditions and using the same feed as in Example I, with the exception that the outlet temperature was 602 F. and the steam to hydrocarbon weight ratio was 0.33 and the feed rate in pounds per hour was approximately 5.1. In one of these runs no recycle was returned while in the other run a recycle stream was returned to the thermal cracking zone. The amount of recycle and the composition of the recycle stream were the same as in Example I. The results of these two thermal cracking runs are given in the following table.

Consideration of Examples I and 11 above clearly demonstrates the ellicacy of the present invention. In both Examples I and II, in the runs in which recycle was returned to the thermal cracking zone, a significant increase in the ultimate yield of the C C olefin hydrocarbon fraction is apparent.

The stream which is recycled to the thermal cracking zone in accordance with the present invention includes all of the liquid olefinic materials of the cracked product containing less than 11 carbon atoms. Such material includes not only mono-olefins, but also diolefins and triolefins and in some instances small amounts of aromatic hydrocarbons. Further, since in most instances it will be impossible to affect a complete and perfect separation between those olefin hydrocarbons containing 10 or less carbon atoms and those of 11 carbon atoms and greater, there generally will be a small amount of olefinic material above C in the. recycle fraction. The amount of such material will, of course, depend upon the efliciency of the distillation or other method of separation employed to make the split between C and C olefinic materials. In most instances, distillation of the cracked oil product obtained from the thermal cracking zone to an overhead temperature of approximately 60 C. at 10 mm. Hg will be adequate for splitting the cracked oil product into a recycle fraction containing olefin hydrocarbons of 10 carbon atoms and less and a product fraction containing olefin hydrocarbons of 11 carbon atoms and greater. Generally in the practice of the present inven tion it will be preferred to recycle either a -0 olefin fraction or more preferably a C9-C o fraction similar to that exemplified in the above examples. The C C olefin fraction will most often have an initial boiling point of approximately 55 C. at atmospheric pressure while the C C olefinic fraction will generally have an initial boiling point of approximately 60 C. at 100 mm. Hg. Recycling may be carried out by any conventional method. It is only material that the recycle be introduced into the thermal cracking zone in a manner such as to insure relatively uniform dispersion of the recycle throuhgout the thermal cracking zone. The recycle material will preferably be admixed with fresh incoming feed, but may be introduced separately and countercurrently, co-currently or cross-currently.

The amount of material recycled may range from as low as 0.25 to as high as 25% by weight of the total feed to the thermal cracking zone. It is preferred, however, that the amount of recycle be within the range of 1 to 10% of the total feed to the thermal cracking zone.

The feedstocks used in the present process are parafiinic fractions containing 50 to 100% by weight of paraflin hydrocarbons. Preferably, the feedstock will be a paraffin fraction containing 90 to 100% by weight paraffin hydrocarbons. The parafiin hydrocarbons may range from 6 to 70 carbon atoms and higher, but preferably will have 6 to 45 carbon atoms. Also, the paraffin hydrocarbons may be branched or straight chain in structure. The source of the feedstocks to the present invention is immaterial so long as the feedstock itself meets the above standards. In those paraflin fractions containing less than 100% paraffin hydrocarbons, impurities may include any hydrocarbon such as parafiin hydrocarbons of less than 6 carbon atoms, olefins, aromatics, naphthenes and the like as well as diluents and other inert materials.

The thermal cracking may be carried out under various conditions of temperature and pressure. Generally, the temperature is within the range of 400 to 900 C. with temperatures of from 500 to 800 C. being preferred. The pressure, ordinarily, is within the range of from atmospheric to 1000 p.s.i.g., but preferably within the range of to 300 p.s.i.g. Usually, the thermal cracking of paraflin hydrocarbons is carried out in the presence of an inert diluent, preferably steam. When an inert diluent is used it is generally used in an amount of 0.1 to 2.0 parts by weight of diluent per part by weight of hydrocarbon feed; Preferably, a diluent to hydrocarbon weight ratio of 0.2:1 to 08:1 is used in the present invention.

In carrying out the practice of the present invention, space velocities of 0.5 to parts by volume of feed per hour per volume of internal reaction space generally are used. However, it is preferred that the space velocity be within the range of 2 to 6 parts by volume of parafiinic feed per hour per volume of internal reaction space.

As previously indicated, the recycle stream containing olefinic hydrocarbons of 10 carbon atoms and less generally is separated from the cracked oil product obtained from thermal cracking by distillation. The distillation is accomplished by conventional methods using conventional distillation equipment such as tray, bubble cap,

packed columns or the like. Distillation may be carried out at subatmospheric pressures or at atmospheric pressures. Ordinarily, this distillation will be carried out at subatmospheric pressures with pressures of 1 to Hg being preferred. It is, of course, understood that where separations of the cracked oil product or the recycle stream are made to narrow the recycle stream by excluding olefinic hydrocarbons of, for example, less than 9 carbon atoms or less than 6 carbon atoms, the above preferred pressures may be somewhat less preferred. The method of distillation, as well as pressures and other conditions are not to be held limiting to the present invention since the choice of such methods to provide the desired splits in the cracked oil product are well within the ability of those skilled in the art. Temperature ranges of several recycle fractions are presented hereinabove. With these teachings, one skilled in the art will find little dificulty in providing the equipment and conditions for obtaining these recycle fractons by distillation.

The equipment which may be used in carrying out the present invention is not critical. Any conventonal thermal cracking equipment may be used. It is only necessary that the equipment be such as to Withstand the pressures and temperatures of the reactions and that the equipment follow good engineering principles.

What is claimed is:

1. In the process of thermally cracking paraifinic feedstocks to produce olefin hydrocarbons suitable for alkylation of aromatics to produce alkyl aromatics for detergents, the improvement which comprises recycling olefin hydrocarbons containing less than 11 carbon atoms to the thermal cracking zone.

2. The process of claim 1 wherein said parafiinic feedstock contains at least 50% by weight of paraffin hydrocarbons of no less than 6 carbon atoms per molecule.

3. The process of claim 1 wherein the thermal cracking is carried out at a temperature of 400 to 900 C.

4. The process of claim 1 wherein the thermal cracking is carried out at a pressure of atmospheric to 1000 p.s.i.g.

5. The process of claim 1 wherein the thermal cracking is carried out in the presence of an inert diluent.

6. The process of claim 5 wherein the inert diluent is present in a weight ratio of inert diluent to paraflinic feedstock of 0.1:1 to 20:1.

7. The process of claim 5 wherein the inert diluent is steam.

8. The process of claim 1 wherein the amount of olefin hydrocarbon recycled to the thermal cracking zone is 0.25 to 25% by weight of the total feed.

9. The process of claim 1 wherein the improvement comprises recycling olefin hydrocarbons of 6 to 10 carbon atoms per molecule to the thermal cracking zone.

10. In the process of thermally cracking parafiinic feedstocks to produce olefin hydrocarbons suitable for alkylation of aromatics to produce alkyl aromatics for detergents, the improvement which comprises recycling olefin hydrocarbons having 9 and 10 carbon atoms per molecule to the thermal cracking zone.

11. The process of claim 10 wherein said parafiinic feedstock contains at least 50% by weight of paraffin hydrocarbons of no less than 6 carbon atoms per molecule.

12. The process of claim 10 wherein the thermal cracking is carried out at a temperature of 400 to 900 F.

13. The process of claim 10 wherein the thermal cracking is carried out at a pressure of atmospheric to 1000 p.s.i.g.

14. The process of claim 10 wherein the thermal cracking is carried out in the presence of an inert diluent.

15. The process of claim 14 wherein the amount of inert diluent is in a weight ratio of inert diluent to paraffinic feedstock of 0.1 :1 to 2.0: 1.

16. The process of claim 14 wherein the inert diluent is steam.

17. The process of claim 10 wherein the amount of olefin hydrocarbon recycled to the thermal cracking zone is 0.25 to 25% by Weight of the total feed.

18. In the process of thermally cracking parafiinic feedstocks to produce olefin hydrocarbons suitable for alkylation of aromatics to produce alkyl aromatics for detergents wherein cracking temperatures of 500 to 800 F. and pressures of 5 to 300 p.s.i.g. are employed and wherein the cracking is carried out in the presence of steam in an amount of 0.1 to 2.0 parts by weight of steam per part by weight of feed, the improvement which com- References Cited by the Examiner UNITED STATES PATENTS 2,945,076 7/1960 Pardee 260683 ALPHONSO D. SULLIVAN, Primary Examiner. 

1. IN THE PROCESS OF THERMALLY CRACKING PARAFFINIC FEEDSTOCKS TO PRODUCE OLEFIN HYDROCARBONS SUITABLE FOR ALKYLATION OF AROMATICS TO PRODUCE ALKYL AROMATICS FOR DETERGENTS, THE IMPROVEMENT WHICH COMPRISES RECYCLING OLEFIN HYDROCARBONS CONTAINING LESS THAN 11 CARBON ATOMS TO THE THERMAL CRACKING ZONE. 